We received the following notification describing an email falling into a Spam Trap. Has anyone else encountered this? If so, what steps can we take to mediate the problem? Also, how do we avoid having this problem again in the future?

Hitting a spam trap isn't good. It's most commonly something that happens when you're sending emails to rented/bought lists (i.e. people who haven't asked to receive emails from you) or leads in your database that are very old and haven't engaged with you in a very long time. Hitting a spam trap signals to email clients and people who subscribe to blacklists for internal blocking that this sender is likely "spamming" - sending emails that are not relevant to people who didn't ask for them.

The Marketo team will probably be able to tell you what the subject line of the email was, but they won't be able to tell you what the email address of the spam trap is, so usually the best practice for avoiding spam traps is to implement well defined processes around engagement and deliverability. Here's a few good resources to look at: